Objectives Attention deficit hyperactivity disorder (ADHD) is a neurobehavioral development disorder contributed to social difficulties and affective problems. ADHD was evidently related to perceived stress, internet addiction and depression, leading to academic problems. However, ADHD symptoms among young medical student remains underreported. This study aimed to investigate the prevalence of ADHD and explore the association between ADHD symptoms and mental health-related conditions among medical students. Results Among 124 participants of first year medical students in Chiang Mai University, Thailand, 78 (62.9%) were female. The average age was 18.7 (SD 0.7). Thirty-one (25%) were considered as having ADHD symptoms based on the Adult ADHD Self-Report Scale screener (ASRS). The group with ADHD symptoms showed higher scores on the internet addiction test core (t = 3.27, p = .001), perceived stress scale (t = 2.94, p = .004) and Rosenberg Self-esteem Scale (t = 3.04, p = .003). No difference was found between groups regarding depression and perceived social support scores. However, the total score of ASRS appeared to significantly correlate with all these mental health- related variables. The relatively high prevalent may have contributed to invalid items of ASRS, for which a new or revised scale is needed.